Canada's medical community could be faced with another shortage of diagnostic isotopes after a further shutdown of the nuclear reactor at Chalk River, Ont.

Atomic Energy of Canada Ltd. said its NRU reactor was shut down last Thursday after a power outage in parts of eastern Ontario and western Quebec.

A heavy-water leak was detected within the facility the following day, and AECL estimates the reactor will be out of service for more than a month while repair options are considered.

The agency said the heavy water is being contained and stored in drums, and there is no threat to workers, the public, the environment or nuclear safety as a result.

The aging facility provides about half the global supply of isotopes used in medical imaging. AECL said it has enough medical isotopes for the coming week, but will be unable to meet demand starting Saturday.

The location of the heavy-water leak, estimated to be at a rate of five kilograms an hour, has been identified at the base of the reactor vessel in a place where there is corrosion on the outside wall of the vessel, AECL said.

This is the latest in a series of problems with the 52-year-old reactor over the past two years — problems that have caused political controversy in Ottawa.

In November 2007, the facility was closed for a few days for routine maintenance. During that time, the Canadian Nuclear Safety Commission discovered emergency backup power wasn't connected to two pumps that prevent a meltdown.

The nearly month-long shutdown that resulted sparked a critical global shortage of medical isotopes used in the diagnosis and treatment of cancer and heart ailments, and only ended when Parliament voted to bypass the regulator.